1. Technical Field
The present disclosure relates to integrated circuits. The present disclosure relates in particular to the field of temperature control of an integrated circuit.
2. Description of the Related Art
Integrated circuits are used to perform many functions and are found in nearly all electronic devices. Integrated circuits are typically formed within and on semiconductor substrates. The physical properties of the semiconductor substrate affect the functionality of the integrated circuit. The physical properties of the semiconductor substrate are in turn affected by the temperature of the semiconductor surface.
Integrated circuits generally comprise numerous transistors formed near the surface of a semiconductor substrate. To form transistors the semiconductor substrate is doped at selected areas with donor and acceptor impurity atoms to alter the conductivity of the semiconductor and to provide the desired carrier type. The electron (a negative charge) is the majority carrier in a semiconductor doped with donor atoms. The hole (a positive charge) is the majority carrier in a semiconductor doped with acceptor atoms. The current and voltage characteristics of a transistor depend in part on the effective mobility of the charge carriers.
The physical properties of doped and undoped semiconductor materials are temperature dependent. The mobility of charge carriers in a semiconductor lattice varies with temperature. The conductivity of undoped silicon also depends on temperature. The conductive characteristics of the transistor are heavily dependent on temperature. The switching speed and performance of the transistors are in turn affected by the conductive characteristics of the transistor. The output characteristics of an integrated circuit containing millions or even billions of transistors can be greatly affected by temperature.
Integrated circuits generally comprise many other kinds of circuit elements whose characteristics are also dependent on the temperature. Integrated circuits are formed of many interconnecting metal lines formed within a multilevel dielectric stack. The physical characteristics of the metal lines and the layers of the dielectric stack also depend on temperature. The temperature dependence of all of these components of an integrated circuit makes the output characteristics of the integrated circuit dependent on temperature.
Many factors affect the temperature of an integrated circuit. The very use of an integrated circuit will change its temperature. As an integrated circuit is used, the large amounts of current flowing through the many circuit elements cause the temperature of the integrated circuit to increase. The heat generated by the integrated circuit increases and decreases as the demand on the integrated circuit increases and decreases. Thus an integrated circuit can undergo large changes in temperature based solely on its own performance requirements from moment to moment.
The temperature of the environment in which the integrated circuit is placed can also have a great effect on the temperature of the integrated circuit, particularly in very cold climates. For instance, a user of an electronic device in a very cold location may use the device outside and then bring the device indoors and cause the device to undergo a large change in temperature due to the large change in ambient temperature. These large changes in temperature affect the performance of the integrated circuit.